Extended-Spectrum Beta Lactamase-Producing E. coli in Freshwater Lakes along an Anthropogenic Impact Gradient

The World Health Organization proposed the Tricycle Protocol for harmonized surveillance of extended-spectrum β-lactamase-producing E. coli (ESBL-Ec) among humans, animals, and the environment. We assessed four freshwater lakes along an anthropogenic impact gradient per the environmental surveillance recommendations of the Tricycle Protocol using membrane filtration with TBX agar supplemented with ceftriaxone (TBX-CRO) and Colilert Quanti-Trays (CQT-CRO) supplemented with the same. ESBL-Ec abundance and prevalence, and ESBL-Ec to E. coli ratios were significantly higher in the two highly impacted lakes; however, in the “pristine” bird sanctuary lake, ESBL-Ec were also present. The CQT-CRO format yielded reasonable qualitative (K = 0.603) and quantitative agreement (intraclass correlation coefficient = 0.849) with the TBX-CRO format. Based on random testing of a single colony per sample, CRO performed poorly for screening the ESBL phenotype among E. coli environmental isolates. Notably, ESBL-Ec isolates were not associated with an increased number of resistance phenotypes compared with non-ESBL isolates. Instead, the number of resistance phenotypes was associated with the lake from which the sample was collected. Our experience suggests when ESBL-Ec are abundant, such as in high-burden settings, the usefulness of the phenotype as a proxy for antimicrobial resistance in the environment is greatly diminished.